Method and machine for cutting corners off sheet material

Abstract: In a method and a cutting machine according to the invention a pile (1) of sheets can be placed on a feeding plane and then carried into a given position in the cutting machine, wherein a pressing foot (7) secures the pile (1) while four cutting knives (11) are pressed down through the corners (24) of the pile against lower knives (12), which ensures a high cutting capacity and a perfect cutting result, the cutting being uniform in the entire height of the pile (1). The machine may be built up with an adjustable part to the effect that the machine can cut in different widths of sheet, and the individual knives (11, 12) may be adjustable for different lengths of sheet. A universal machine is thus provided, which is easily and quickly adjusted for different formats, in addition to which it is easily operated since the pile (1) can be inserted, cut and removed through the machine in a continuous procedure.

Description: Prior art technique The invention relates to a cutting machine according to the preamble of claim 1. An application example of material in the form of a sheet, e.g. of metalfoil coated cardboard with cut off corners is a base for food articles, such as sliced fish or meat, which is subsequently wrapped into a transparent plastic film to form a sales package. The rounded corners provide a pleasant impression of the appearance of the package, and at the same time the rounded corners protect against damage to the plastic film, in particular where the film is shrinked onto the package. Furthermore, the rounded corners are used as a natural shape for e.g. playing cards and other cards, which should be easy to handle, and where sharp corners would be uncomfortable. Finally, books might be mentioned, including telephone books and other directories, where sharp corners would be worn or bent while rounded corners provide an ideal shape for the pages. Such rounded corners are normally produced in a cutting machine. An example of a machine of this type is known from DE Printed Specification no. l.268.588, which relates to a machine capable of rounding off all four corners in one operation. This is accomplished by means of four knives, which are moved down simultaneously, thereby cutting off the corners of rectangular sheets. This known machine is preadjusted for a specific format size, for instance playing cards. A pile of rectangular cards are positioned in a tray having a lateral guide, and four knives with press rams are then moved downwards, cutting off the four corners. After completion of the cutting operation the knives and the press rams are raised, whereupon the ready-cut cards can be removed from the tray, and a new pile placed into position. The cutting procedure is accomplished alone by means of four movably mounted knives which sets a limit to the height of the pile and thus the cutting *p+2Xcapacity of the machine, because the cutting procedure becomes unprecise and the cuts of inferior quality if the pile gets too high. This drawback is mainly a result of insufficient control of the knives near the processing area. In view hereof, the machine has limited applicability because it is partly limited for use for particular formats, partly for manual feeding and removal of the pile of sheets, and finally the machine has a cutting capacity, which is limited to a comparatively low pile. From US patent No. 3,125,920 is furthermore known a corner cutting machine according to the preamble of claim 1. Another machine for rounding the corners on stacks of paper is known from US patent No. 3,656,387. This machine is handoperated and is not able to cut all four cornes of the stack in one operation. It has, however, lower knives under the cutting knives. It is a common drawback to the above named known machines that the edge of their cutting knives extends in a plane parallel with the sheets whereby each edge forces its way through a sheet with the total length of the edge in action at the same time. In this way it is not possible to make a real clean and proper cut. Object of the invention It is an object of the present invention to remedy the above described drawbacks and limitations of the known cutting macines for cutting corners off a pile of sheets, and this object is achieved by providing for the cutting machine defined in claim 1. The cutting edges of the cutting knives extend along an upwardly directed arc between the outermost points of the cutting edge of the knives, said cutting knives being tapered to form a wedge, the tips of which are constituted by the lowermost points of the edge, whereby the extreme pointed ends thus extending like spearheads through the pile. The edge of each knife then forces its way successively through a sheet and the intermediate and underlying material is compressed during the cutting operation itself, resulting in a precise and clean cut. A cutting machine of high capacity, which is up to now unknown, is thus provided to the effect that the height of the pile can be up to 500 mm with a perfect cutting result, which is in part due to the combined cutters comprising a cutting knife and a lower knife, ensuring a uniform cut through the entire pile, and in part due to the pressing foot being pressed down to ensure that the pile is firmly secured during the cutting operation. In addition to the increased cutting capacity and the perfect cutting result, the task is simplified by the continuity which the machine allows for in that a pile can be fed into the machine, proceed on the same level inside the machine and, after completion of the cutting operation, move out through the opposite end of the machine. The cutting operation can thus be automated, the machine becoming a continuous machine, thereby reducing running costs considerably. Fast feeding and removal is ensured by letting a new pile push the ready-cut pile out of the machine, increasing the productivity of the machine and reducing manual labour in relation to the cutting operation. By constructing the machine so that the knives are adjustable according to the width as well as the length of the pile, it becomes possible to cut different sizes of sheet in one machine, the machine being adjustable by means of a simple adjustment device. An up to now unknown degree of adaptation in accordance with different sizes of sheets has thus become possible, without compromising the excellent cutting properties of the machine. By mounting each cutting knife on a knife holder and mounting the holder on a beam or a head, which is slidable on a die set by means of a drive motor, perfect control and depression of the knives is guaranteed, in addition to which the distance between the knives is adjustable by regulating the knife holders. By mounting each lower knife on a holder provided with a control, the cutting knife sliding on the said control, a perfect cutting result is guaranteed, including a clean cut and a cut which is gentle on the knives, due to the precise interaction between the cutting knife and the lower knife. By cutting in a sector of a circle, whereby the lower knife may be formed like a circular disk-shaped knife, which can be rotated when it is worn, a considerable reduction of running costs as well as of the number of tool replacements are achieved. The drawing The invention will be described below with reference to the drawing, wherein Fig. 1 illustrates a cutting machine according to the invention without the pile of sheets, Fig. 2 illustrates, in a simplified form, a pile of sheets during its feeding into the machine, Fig. 3 illustrates the pile having been fed into the machine and with the pressing foot pressed down, Fig. 4 illustrates the pile during the cutting operation, Fig. 5 illustrates the pile moving out of the machine Fig. 6 illustrates details of the cutting knives and how they are controlled, Fig. 7 illustrates the cutting knives being pressed down and in the process of cutting, Fig. 8 illustrates the shapes of the set of knives, and Fig. 9 illustrates the interaction of the set of knives. Description of an embodiment of the invention An example of a cutting machine according to the invention is illustrated in Fig. l. The machine is built up on a frame with legs, and the transfer and cutting units are built on said frame. The transfer unit comprises a feeding plane, which is illustrated on the left side of the frame, said plane being provided with a longitudinal guide 2 extending in the direction of transfer of the machine, and is so adjusted than a pile of sheets, which is not illustrated, can be placed on the feeding plane with one lateral face resting against the guide 2. An arm 3, moved by a drive motor, which is not illustrated, then pushes against the rear edge of the pile, thereby pushing the pile into the cutting unit itself. The cutting unit is made up of two sections, the distance between which is adjustable according to the width of the pile. Each section comprises a cylinder 8 provided with a ram press, which is connected to a bridge or a beam 9 being slidable in upwards and downwards direction on a die set 10, which rests on the base of the frame. At the lower end of the die set are provided distance bushes 18 to restrict the downwards movement. The drive motor 8 is mounted on a fixed bridge or beam 20, resting against the die set l0. The distance between the two sections is adjustable by means of a handwheel 17 to the effect that the machine can be is adjusted to the desired cutting width of the pile. Four guides 4 are provided for guiding the pile into the machine, and the pile is placed between these guides. In order to restrict feeding of the pile into the machine and to determine the position of the pile, and end stop 5 is provided, which can be raised or lowered by means of a work motor 6. The position of the end stop is adjustable, its motor 6 with carrier being movably mounted in a track 21 of the top bridge 20 and secured hereto. When the pile has been positioned in the machine between the guide 4 and the end stop 5, a pressing foot 7 is pressed down by means of a work motor, said pressing foot being formed like a plate, which compresses the pile and secures it firmly during the subsequent procedure. Finally, the cutting unit itself comprises four cutting knives, each secured to its knife holder 26, which is movably mounted on the bridge 9 of the knife holder. The distance between the cutting knives is thus adjustable according to the length of the pile. Each set of knives comprises a lower knife 12, which is secured in a holder 13, said holder also carrying a die set l4 for the holder 26 of the cutting knves to the effect that a precise control and thus precise interaction is guaranteed between the individual upper and lower knives of each set of knives. Each holder 13 is movable between a guide track l5 and guide portion of the base to the effect that the distance between the sets of knives can be adjusted precisely in the longitudinal direction of the machine. At the opposite side of the feeding place is mounted a conveyor 22, capable of carrying the ready-cut pile away from the cutting unit. Finally, a box 23 is mounted on the frame, with the electric controls being built in, to control the individual functions of the machine by means of commonly known hydraulic and/or pneumatic controls for the drive motors. The cutting machine is functioning as described below with reference to Fig. 2-9. The cutting machine is adjusted according to the current dimension of the pile so that the sets of knives 11, 12 are positioned exactly at the corners 24 of the pile l, when the pile l, as illustrated in Fig. 2, is placed in the machine between the guides 4 and the end stop 5, as illustrated in Fig. 3. In this position the pressing foot 7 is pressed down to the effect that the pile 1 is firmly secured and compressed in the cutting position. The cylinders 8 are then activated, and the upper knives of the bridges 9 are pressed down through the corners 24 of the pile. The corners having been cut off, the bridges 9 with the cutting knives 1l are raised, and the pressing foot 7 and the end stop 5 are raised at the same time in order that the pile 1with its cut off corners can be moved out onto the conveyer 22, as illustrated in Fig. 5. This is achieved in that the pile 1 is pushed out by meansof the transfer device 3 carrying a new pile l into the machine for cutting. The cutting procedure may then be repeated, and corners can be cut off in a continuous, automated process. In the above described manner it is possible to cut up to 30.000 sheets per hour, by far exceeding the capacity of the machines known up to now. To achieve a production of such capacity is especially the result of the precise control of the movement of the knives and the design of the set of knives itself. As illustrated in Fig. 6, the cutting knives 1l are mounted on the holder 26, which is controlled by the die set 14, which for its part is firm with the lower knife 12. The cutting knife 11 is hereby controlled in its entire length of stroke, and a completely uniform cut of the corners 24 is achieved, the control of which extends in the entire length of cutting. Fig. 7 illustrates how the pointed edges 25 of the cutting knives 11 keep the sheets of the pile 1 in a fixed position to the effect that the subsequent cutting of the corners 24 is effected in a condition wherein corner material is compressed and under tension as compared to the cutting edge of the cutting knife l1. As illustrated in Fig. 8, the cutting knives 11 are provided with a notch, which is shaped like a sector of a circle, and since the knives at the same time are wedge-shaped, the pointed end 25 illustrated in Fig. 7 is formed with an intermediate circular edge extending in an arc. When this edge needs sharpening it can be done by simply grinding the diagonal underside. The lower edge is illustrated in Figs. 8 and 9. It is configured as a circular disk 27 of essentially the same diameter as the cutting knife ll. A screw 28 secures the disk 27 to the holder l2 so that when the circular edge 27 is worn, the screw 28 can be released, whereupon the knife 27 can be turned by means of a handle with a pin in the holes 29, until a new edge 30 is carried forwards under the cutting knife ll. By means of this extremely simple design of the set of knives, it is possible to cut precisely and uniformly through a pile of sheets up to a height of 500 mm and without much strain on the cutting edges, whereby the tool life becomes quite high. In addition hereto, the quality of the cutting is high to the effect that the rounding of corners becomes uniform in the entire height of the pile.

Claims: A cutting machine for automatically cutting of corners (24) of a pile (1) of preferably identical rectangular sheets of material, especially of cardboard, paper, fabric, plastic, metal foil and combinations of such materials, with four cutting knives (11) being movable between a free position above the pile (1) and a lower position, whereby the machine comprises; a feeding plane for placing the pile (1) such that it is resting with one lateral face against a guide (2) extending in an longitudinal direction of the machine; a first moving means (3) for moving the pile (1) along the guide (2) in the longitudinal direction of the machine into a cutting unit; a pressing foot (7) movable to and fro between a free position above the top of the pile and a securing position in which the pressing foot (7) is being pressed down upon the top of the pile (1); means for moving the pressing foot (7); means (8) for moving the cutting knives (11) to and fro between a free position above the top of the pile and the lower position, all four corners (24) of the pile (1) being cut simultaneously when the cutting knives (11) are moved downwards from their free position to their lower position; and second moving means (22) for moving the pile (1) out of the cutting unit, into the same direction as the pile was moved into the cutting unit, after the pressing foot (7) and the cutting knives (11) have been returned into their respective free positions by their respective means, characterized in that lateral guides (4) are provided in the cutting unit for guiding the pile (1) when it is being moved into position into the cutting unit, an end stop (5) being being provided which is movable by means (6) between a stop position in which it can be abutted by the front side of the pile and a free position above the pile the first moving means (3) moving the pile until the front side of the pile abuts the end stop (5); in that four lower knives (12) are provided, one under each corner of the pile, for supporting the pile during cutting, the shape of the lower knives (12) being substantially complementary to the shape of the cutting knives (11) in the regions along which the cuts are made, such that the cutting knives (11) and the lower knives (12) can cooperate to provide a shearing action by moving the cutting knives into a position in which their cutting edges are below the upper surfaces of the lower knives, and in that the cutting edges of the cutting knives (11) are extending along an upwardly directed arc between the outermost points (24) of the cutting edge of the knives said cutting knives (11) at the same time each being tapered to form a wedge-shaped cutting edge. A cutting machine according to claim 1, characterized in, that the cutting unit comprises two cutting sections (8, 9, 10) each provided with two sets of knives (13, 14, 26) having a cutting knife (11) and a lower knife (12), the distance between said cutting sections being adjustable according to the width of the pile (1), and the distance between the sets of knives of each cutting sections being adjustable according to the length of the pile. A cutting machine according to claim 2 or 3, characterized in, that each cutting knife (11) is mounted on a knife holder (26), which is secured to a beam (9), which can be moved, sliding on a die set (14), by the ram press of a work cylinder. A cutting machine according to claim 3, characterized in, that each lower knife (12) is mounted on a holder (13), which is provided with a vertical control (14) for the holder (26) of the cutting knives. A cutting machine according to claim 1 - 4, characterized in, that the cutting form of the knives (11, 12) is a segment of a circle, and that the lower knife (12) is formed like a disk (27) having a circular edge (30), which can be rotated about its centre axis (28) and is secured to its holder (12).

Inventors: OLESEN JERRY MALLING, OLESEN, JERRY MALLING
Applicants: GRAFISK REPARATION SERV APS, GRAFISK REPARATION & SERVICE APS
Application year: 1994
Main classification: B26D3
IPC codes: B26D3, B26D7